1. Field of Invention
The invention relates to a cartridge stopper with a valve function, especially for printing ink cartridges made of plastic.
2. Description of Related Art
Modern printing presses use continuously controlled automatic ink feed to the fountain. For this purpose, plastic cartridges filled with ink are placed in pneumatic extrusion devices mounted on the printer fountain that extrude ink pneumatically pulsewise into the fountain in the quantities required. The cartridges have a cartridge stopper with a valve function (i.e., it also functions as a valve).
Known cartridge stoppers of this type include elastic sealing membranes that act as valves and are cut in a stellate or simple diametral fashion. Such stoppers open when pressure is exerted on the cartridge contents and automatically close again by elastic return when the pressure is relieved. However, such stoppers do not operate satisfactorily as experience has shown.
A number of requirements are placed on such a cartridge stopper with a valve function. For example, to hold and transport the cartridges until they are used and to store opened cartridges until they are used again, the cartridge must be sealed absolutely air-tight to prevent the ink from drying out. Any leak, however small, in the vicinity of the cartridge stopper causes the ink to dry out even to a small extent in the outlet area, clogging the outlet opening and preventing the valve from functioning, and especially making tight re-closure impossible. This poses the unwanted condition of ink cartridges that are still mostly full, becoming useless. This is especially serious when only small quantities of one color are required (at any particular time) for multicolor printing.
Additionally, when the color cartridge is in use, application of pneumatic pressure to the extruding piston is intended to open the seal in order to allow ink to escape and then to close it again as tightly as possible. This function is extremely important for the use of printing ink cartridges in presses with continuously controlled automatic ink feed to the fountain since the ink cartridges remain in place in the pneumatic extrusion devices throughout printing and must supply ink to the fountain without dripping, and in particular with no air being allowed to enter the cartridges between ink extrusion pulses as a result of leaks at the cartridge stopper.